Wrap spring clutch



Dec. 1, 1964 H. F. WELSH ETAL 3,159,255

WRAP SPRING CLUTCH Original Filed April 27, 1956 5 FIG. 1A

' DETENT ARM 81 @1 T5 OUTER WRAP SPRING RATCHET POWER SHAFT '(0 annnnuun0,11,11,11,

ROTATION OUTPUT SHAFT 72 |NNER WRAP DETENT RING SPR|NG INVENTOR. H. F. WELSH N. J. APPLETON BY M. SILVERBERG United States Patent 3,15%256 WRAP SPRING CLUTCH Herbert Frazer Welsh and Norman .l'. Appleton, Philadelphia, and Morton Silverberg, liliiins Park, Pa, assignors to Sperry Rand Qorporation, New York, N.Y., a corporation of Delaware Brigittal application Apr. 27, 1956, Ser. No. 581,235, new Patent No. 3,i)21,512, dated Feb. 12, 1962. Divided and this application June 20, 1961, Ser. No. 124,268

2 Claims. (Cl. 192-81) This application is a division of co-pending application Serial No. 581,235, filed April 27, 1956 entitled Selector Mechanisms, now Patent No 3,021,512, issued Feb. 12, 1962.

This invention relates to wrap spring clutches, and, in particular, to such clutches which are actuable by electrical control pulses.

Servo-mechanism controlled positioning mechanisms, and selector mechanisms such as described in our aforesaid patent, employ various types of pulse or signal responsive actuators. A preferred form of the invention utilizes selectively actuated wrap spring clutches of novel design.

An object of the present invention resides in the provision of an improved wrap spring clutch.

Another object of the present invention resides in the provision of an improved wrap spring clutch capable of actuation by electrical control pulses.

The foregoing objects, advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings, in which:

FIGURE 1A illustrates an improved wrap spring clutch constructed in accordance with the present invention;

FIGURE 13 is a view taken on line B-B of FIG- URE 1A;

FIGURE 1C illustrates an alternative ratchet and stop mechanism for a wrap spring clutch such as may be employed in the present invention; and

FIGURE 1D illustrates a further portion of another alternative form of wrap spring clutch such as may be employed in the present invention.

In the servo-positioning devices of the prior art, many forms of actuating members have been used. One such actuating member is the solenoid, and this has been very popular in devices of this type. However, it has been found that in servopositioning systems, a preferred actuator takes the form of 180 revolution clutches, and the elements to be moved, such as rotatable pulleys, are eccentrically mounted on an output shaft of such halfrevoiution clutches for moving the said pulleys to their said binary positions, thereby to alter the effective length of cable and the effective position of the work piece or transducer.

It is noted that a 180 clutch is one which, upon being pulsed with the proper signal, proceeds to rotate from one fixed position to another position 180 away. A- tached fully rotating pulleys, eccentric to the axis of rotation of the clutch, will therefore displace through a distance equal to twice the eccentricity. The output motion, due to each clutch, is basically sinusoidal; and if the clutches are started at the same time and have the same r.p.m., the full output is basically sinusoidal. This means that the output is started at maximum acceleration and zero velocity, is then brought up to maximum veloc- ,lddjdd Patented Dec. l, 1964 Another important benefit deriving from the use of a clutch of the aforementioned type, is that the eccentric loading matches the impedance of the input power source and of the output. At the beginning and end of a cycle, when the forces are high (and the velocity is low) the pulley is near top dead-center giving the clutch a large mechanical advantage. At the mid-stroke (when the acceleration is near zero), the mechanical advantage is in favor of the cable. The design of the clutch accordingly becomes an important factor in the total mechanical selector unit and one type of clutch known as the wrap spring clutch is particularly suited for this type of service. A preferred form of such wrap spring clutch is illustrated in FIGURE 1A; and it will be noted from the subsequent description that some of the elements comprising this clutch diifer from conventional wrap spring clutches. 7

Thus, referring to FIGURE lA, it will be seen that in accordance with the present invention, an actuator taking the form of a wrap spring clutch may comprise a power shaft 7%) which is constantly rotated by a motor 71; and an output shaft 72. is disposed collinear with the power shaft 76 and spaced therefrom. An outer wrap spring 73 is placed about the power shaft 7% and output shaft 72, and the turns of the said spring 73 are divided between the said output shaft and the power shaft. A ratchet 74 (the configuration of which is more easily Seen in FIGURE 1B) is carried by the power shaft 7t) and is adapted to be capable of free rotation on the said shaft 70. Spring'73 is coupled at one of its ends to the said ratchet 74-, and is coupled at the other of its ends to output shaft 72.

In the design of the clutch, the diameters of the power shaft 7% and output shaft 72 are the same, and the natural internal diameter of spring 73 is somewhat smaller than the diameters of the shafts 7i and 72. A pulse-responsive interposer or latch 75 is coupled to the ratchet 74 and is held in position adjacent the said ratchet 74 by a spring 76 whereby, in the absence of pulse input at terminals 77, the interposer 75 restrains rotation of the ratchet 74. In this condition of operation, therefore, the outer wrap spring 73 is caused to exhibit a somewhat larger internal diameter than the diameters of shafts and 72; and no power is transferred through the spring 73 to the output shaft 72 from the constantly rotating power shaft 70.

If now a pulse input should appear at terminals 77, the interposer will be pulled downward thereby releasing the ratchet 74. The wrap spring 73 will thereupon engage the outer peripheries of power shaft 7d and output shaft 72, and will drive the output shaft forward with a torque equal to where P is the interference pressure, r is the radius of the shafts 7t) and 72, w is the width of each wrap spring turn, a is the base of the natural system of logarithms, ,u. is the C06fil0l11ll of friction, and p is the number of turns of the wrap spring on the power shaft 7d in radians.

The pulsed interposer 75 will thereafter ride upon the extherefore, when the wrap spring clutch, illustrated FIGURE 1A, is pulsed, the output shaft '72 will define a turn before it is once more caused to stop. During this rotation, a pulley till eccentrically coupled to the output shaft 72 by an arm 82, Will be caused to move al., whereby a workpiece or transducer coupled to that cable will move through an appropriate distance.

In the particular form of wrap spring clutch shown in FIGURE 1A, a smaller or inner wrap spring 83 is disposed internal of the power shaft 70 and output shaft 72, with the turns of the said spring 83 again being divided between the said shafts 70 and 72. The direction of Winding of spring 83 is opposite to that of drive spring 73; and in practice, the spring 83 will slip so long as the power shaft 70 is turning faster than the output shaft 72. If, however, the output shaft 72 should attempt to turn faster than the power shaft 70, the inner spring 83 engages, thereby preventing the output from going faster than the chosen rpm. of the power shaft 70.

The stopping torque for the wrap spring clutch, illus- 'trated and described in reference to FIGURE IA, is

provided by a detent system comprising a detent ring 84 carried by the output shaft 82 and cooperating with a pair of detent arms 85. This configuration will be more readily apparent from an examination of FIGURE 13; and it will be seen that the detent ring 84 preferably includes one or more detent notches 86 and 37, machined into the said ring 34'. The detent notches 86 and 87 cooperate with a pair of roller followers 88 and 89 carried respectively by the pairof detent arms'85; and the said detent arms 85 are pivotally mounted at points 90 and are spring-loaded by a spring'9l, whereby the roller followers 88 and 89 are urged toward one another 'into the detent notches 86 and 87. When the drive clutch spring 73 (FIGURE 1A) is engaged by pulsing of the actuator interposer 75, suflicient torque is developed to both accelerate the clutch and to drive it out of its detent position. The output shaft 72 then proceeds to rotate at some specified r.p.m. defined by motor 71, through substantially 180, in the manner already described; and as this rotation approaches its 180 position, the detent rollers 88 and 89 start to descend'the' detent notch walls defined by notches 86 and 87. The

notches.

If the energy product of the depth of the detent notch and the spring load afforded by spring91 is greater than the energy contained in the rotation of the clutch, the

inner wrap spring 83 does not allow any over-speed of clutch cannot go past its detent position,- and is thus trapped. It is of interest to note that since'the free end of the drive spring (that is'the end of the spring attached to ratchet 74) is preventedfrom rotating from a point prior to the zero position of the detent notch, the spring 73 is unwrapped from the shafts 70 and 72 in a stauc position, and this consideration serves to minimize the wear on the wrap spring 73.

When it is desired to operate a clutch for a shorter cycle time than that already described, and when the stroke of the clutch need not be large, it is possible to operatethe clutch through less than 18Q" in response to a pulse input. The ratchet 74, described in reference to FIGURE 1A, may accordingly be replaced bya ratchet such as 92, shown in FIGURE 1C. This particular ratchet'includes' four steps (rather than the two steps of ratchet 74), said four steps being equiangularly spaced from one another and cooperating with 'a pulse respom sive interposer, generically illustrated at 3. By reason of this configuratiomtherefore, the application of a control pulse to the pulse responsive interposer93 permits the cllll h to Operate through only 90 degrees (father ,tion of said input shaft to said output shaft.

when the four-step ratchet 92 is employed, the detent ring (similar to 84) should also have four, rather than two, spaced detent notches (similar to 86 and 87).

While the form of wrap spring clutch described in I reference to FIGURE 1A has one end of the spring 73 connected to the output shaft 72, it should be noted that this is not necessary; and if desired, the said one end of spring 73 may be coupled to a mass 94 (see FIG- URE 1D), rather than to the shaft 72 itself. This alternative configuration achieves certain appreciable benefits. Thus, the important adjustment in respect to the relationship between the down slope of the detent notch and the detent roller at the moment when the set or step in the ratchet strikes the interposer, such as 75,'is now done automatically and continuously.

If the interposer should strike its appropriate ratchet step before the detent roller has reached the detent notch, the spring 73 will stand still as the output comes to a stop. Each time the clutch is pulsed, the leading condition of the wrap spring is decreased until the roller 7 falls into the detent shortly after the release of the drive spring. It should further be noted that, if for some reason such as wear, slippage, or initial adjustment, the opposite condition exists, ie the bottom of the detent notch leads the step of the ratchet, the action of mass 94 rectifies this error over a series of cycles; and each time the clutch stops, the mass 94 causes the spring 73 to unwind and shift forward a small amount. of operational cycles, therefore, the detent roller walks its way down the up-slope of the detents and the two actions then stabilize one another.

Wrap spring clutch actuators, generally of the type described in reference to FIGURES .1A, 1B, 1C and 1D find particular utility in pulley and cable type selector mechanisms, and a preferred form of selector mechanism utilizing such clutches is illustrated in FIGURE 2 of our 7 aforesaid US. Patent No. 3,021,512.

have been described, it will be appreciated that many variations will be suggested to those skilled in the art, in accordance with the principles discussed. The foregoing description is therefore meant to be illustrative only and is not limitative of our invention; and all such variations as are in accord with the principles described, are meant to fall within the'scope of the appended claims.

Having thus described our invention, we claim: 1.'A wrap spring clutch comprising a hollow cylindrical input shaft, a hollow cylindrical output shaft substantially coaxial with said input shaft and spaced axially therefrom a ratchet rotatably mounted relative to one of said shafts, a first spring disposed adjacent the exterior surfaces of both said input and output shafts and connected at one of its'ends to said ratchet, a second spring I disposed to engage the interior surface of both said input and output shafts when said output shaft overruns said ing said first spring to engage the exterior surfaces of I said input and output shafts thereby to transfer the rota- 2. A wrap spring clutch comprising an input shaft, an output shaft substantially coaxial with said input Over a series shaft, a Wrap spring for engaging said input and output shafts to couple said output shaft to said input shaft to be driven thereby, signal responsive detent means for References Cited in the file of this patent UNITED STATES PATENTS engaging the end of said wrap spring adjacent said input 1,629,420 Starkey May 17, shaft to disengage said spring from said input shaft, 5 2,039,807 Momau Aug 10, detent means for engaging said output shaft to position 2,161,941 Inna said output shaft with respect to a certain reference, the 2,475,432 Marlllar't July 5, output end of said wrap spring being free to move around 2,794,524 m} et June said output shaft, and a mass connected to the output end 2,829,743 saflchlm et a Apr. 8, of said Wrap spring whereby said spring and output shaft 10 2,895,578 Wmchen y detent means are self adjustable. 

1. A WRAP SPRING COMPRISING A HOLLOW CYLINDRICAL INPUT SHAFT, A HOLLOW CYLINDRICAL OUTPUT SHAFT SUBSTANTIALLY COAXIAL WITH SAID INPUT SHAFT AND SPACED AXIALLY THEREFROM, A RATCHET ROTATABLY MOUNTED RELATIVE TO ONE OF SAID SHAFTS, A FIRST SPRING DISPOSED ADJACENT THE EXTERIOR SURFACES OF BOTH SAID INPUT AND OUTPUT SHAFTS AND CONNECTED AT ONE OF ITS ENDS TO SAID RATCHET, A SECOND SPRING DISPOSED TO ENGAGE THE INTERIOR SURFACAE OF BOTH SAID INPUT AND OUTPUT SHAFTS WHEN SAID OUTPUT SHAFT OVERRUNS SAID INPUT SHAFT, SAID SECOND SPRING BEING ATTACHED AT ONE OF ITS ENDS TO ONE OF SAID SHAFTS, DRIVE MEANS COUPLED TO SAID INPUT SHAFT FOR ROTATING SAID INPUT SHAFT AND SIGNAL RESPONSIVE MEANS COUPLED TO SAID RATCHET FOR SELECTIVELY CAUSING SAID FIRST SPRING TO ENGAGE THE EXTERIOR SURFACES OF SAID INPUT AND OUTPUT SHAFTS THEREBY TO TRANSFER THE ROTATION OF SAID INPUT TO SAID OUTPUT SHAFT. 